1. Field of the Invention
The invention relates to a method for assigning and a method for scheduling codes for data transmissions, between a radio station and at least one subscriber station, over an air interface of a radio communication system, together with appropriate network-side equipment and an appropriate radio station
2. Description of the Related Art
In radio communication systems with a CDMA component (CDMA: Code Division Multiplex Access), use is made of orthogonal codes to enable subscriber stations and/or transmission channels to be distinguished. Examples of orthogonal codes are so-called OVSF codes (OVSF: Orthogonal Variable Spreading Factor), such as are described for example in section 4.3.1.1 of the 3GPP (3rd Generation Partnership Project) Standard document, TS 25.213 V5.5.0 (2003-12). Orthogonal codes can be represented in the form of a code tree, as shown in FIG. 4 for the OVSF codes in the aforementioned standard document. Each level of the code tree corresponds to a spreading factor, and has as many branches as the numeric value of the spreading factor. For example, with a spreading factor of 4 the corresponding level in the code tree has four branches, and each of the codes corresponding to the branches has a length of four bits. With a spreading factor of 16, the corresponding level has sixteen branches and each of the codes has a length of sixteen bits.
Depending on the combination of codes which a subscriber station or a radio station uses simultaneously for data transmissions, there is in each case a resulting maximum signal-to-average ratio (PAR: Peak-to-Average Ratio) for the transmission power. The signal-to-average ratio of the transmission power gives the ratio of an instantaneous value of the transmission power to the transmission power averaged over time.
According to section 9.2.2.1 8F of the 3GPP standard TS 25.433 V5.9.0 (2004-06) radio stations must, for example, use consecutive codes for transmissions using HSDPA (High Speed Downlink Packet Access). This means that the codes which can be used by a radio station must correspond to branches which lie contiguously adjacent to one another at the level in the code tree corresponding to the chosen spreading factor. The radio stations must therefore be configured by manufacturers in such a way that for every possible combination of codes they are always able to adhere to the corresponding maximum possible signal-to-average ratio. This means that the largest possible value of the signal-to-average ratio determines in each case how a transmission power amplifier must be dimensioned for a radio station. Since subscriber stations can also use several codes for transmissions in the upward direction (uplink), there are also different combinations of codes for subscriber stations. Hence, a transmission power amplifier for a subscriber station must also be dimensioned so that it is possible to adhere to a maximum possible signal-to-average ratio.